grabbed headlines this week. florida senator marco rubio, a practicing catholic, tried to walk the line between science and faith-based creationism when asked how old the planet is. here's what he told "gq" magazine. i'm not a scientist, i don't think i'm qualified to answer a question like that. at the end of the today, i think there are multiple theories out there on how the universe was created and i think this is a country where people should have the opportunity to teach them all. i think parents should be able to teach their kids what their faith says, what science says, whether the earth was created in seven days or seven actual eras, i'm not sure we'll ever be able to answer that. it's one of the great mysteries. famed television scientist bill nye joins me now from los angeles. good morning. so you, like other scientists, say that we know how old the earth is and that the topic is not even up for debate. but every so often a politician makes headlines either denying science or casting some doubt here. so tell us, as far as you know, how old is the earth and how do you know it?